1. Q. What is the test performance of the PCR assay in use at PHO Laboratory?

A. PHO Laboratory validated the PCR assay currently in use in close collaboration with the National Microbiology Laboratory (NML), Canada’s reference microbiology laboratory. We have excellent concordance with NML from the parallel testing done with them at set up, which included a large number of negatives (over 100) and positives (over 20). The sensitivity and specificity of the assay, comparing to NML as the gold standard, is close to 100%.

However, there are many commercial and laboratory developed assays being released and used in Canada, and it is not possible to compare assay performance with every one of them. It is expected there will be some variance in performance if multiple assays are compared to each other, especially around the limit of detection of the individual assays. Parallel testing with the commercial kits in use so far shows similar performance with the assay in use at PHO Laboratory.

More information on the testing done at PHO Laboratory from our COVID-19 Test Information Sheet:

https://www.publichealthontario.ca/en/laboratory-services/test-information-index/wuhan-novel- coronavirus

2. Q. What is the positive predictive value of COVID-19 PCR assays?

A. In general, the positive predictive value of COVID-19 PCR assays is excellent, and approaches 100%. At PHO Laboratory, we know this, as we are able to generate viral sequence from samples that are positive provided the viral copy number is not near the limit of detection of the assay.